Frequency control system



April 26, 1949. s. w c 2,468,148

FREQUENCY CONTROL SYSTEM Filed June 16, 1945 s Sheets-sheaf 1- I ENE-'1:IIIS

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' FREQUENCY CONTROL SYSTEM Filed June 16, 1945 s Shets-Sheet 2 JET-'- Il 7 540/250 cs. wac/fmw April 26, 1949. G. s. WACHTMAN FREQUENCY CONTROLSYSTEM 3 Sheets-Shee't 5 Filed June 16,, 1945 v WVI 5 175. 4 A W5 .B mP; W 4. 5.7 a W L7 #vmsvvroe A iron/var Patented Apr. 26, 1949 UNITEDSIZES PATENT OFFICE FREQUENCY CONTROL SYSTEM George S. Wachtman,Harrisburg, Pa.

Application June 16, 1945, Serial No. 599,828

be secured with relatively inexpensive equip- :ment.

Another object of my invention is to provide an electrical tuningcircuit of high efficiency which may be adjusted with ease toselectedfrequencies within a band of frequencies with high precision.

Another object of my invention is to provide an oscillation system thatcan be closely calibrated and which will retain this calibration at anypoint through a specified frequency range.

Another object of my invention is to provide ,a compensation system fora control condenser in an oscillator circuit in which the bandspread orfrequency range of the control condenser may bemade equal at allfrequencies to which the circuit may be tuned.

Other and further objects of my invention reside in the arrangement ofelectrical condensers in association with a tuning inductance as. setforth more fully in the specification hereinafter following by referenceto the accompany ing drawings, in which:

Figure 1 schematically shows a bandspread circuit referred tohereinafter for explaining the operation of the circuit of invention;Fig. 2 shows a modified bandspread circuit hereinafter referred to inexplaining the theory of my invention; Fig. 3 illustrates a form ofbandspread circuit that operates in a manner opposite to tures of myinvention and which combines the i.

circuits of- Figs. 2 and 6; Fig. 8 shows a circuit embodying certain ofthe features of my inven tion and which is a modified form of thecircuit of Fig. 7; Fig. 9 illustrates a circuit arrangement embodyingthe principles of my invention and :1

which includes an oscillator system having compensating means forcorrecting for lack of uniformity of control range of the usualbandspread condenser; Fig. 10 shows a further form of compensationcircuit embodying my invention; Fig. 11 combines the circuits of Figs. 8and 10 in securing more effective compensation .for the bandspreadtuning condenser; Fig. 12 illustrates the circuit of my inventionprovided with adjustment means for correcting the bandspread controlcondenser at the minimum frequency .to.

which the circuit is tunable; Fig. 13. schematically illustrates acircuit arrangement embodying my invention for providing compensationfor the bandspread condenser at its maximum tunable frequency; Fig. 14combines the desirable features of the circuits of Figs. 12 and 13 forproviding greater ease of adjustment in effecting compensation of thebandspread tuningcondenser; Fig. 15 shows an improved arrangement overthat illustrated in Fig. 14 in which simultaneous operation of thecontrol condensers in different parts of the circuit are effected; Fig.16 shows a modification of the circuit arrangement of Fig. 15 includingmeans which arcadjustable to fix the minimum capacity and/or maximumfrequency of the circuit; and Fig. .17 is a further modified form of thecircuit shown in Fig. 16 for obtaining more stabilized and precisionfrequency control.

The improved circuit of my invention .is adapted for use as a variablefrequency oscillator, a signal generator, an exciter unit for atransmitter, a crystal calibrating and finishing oscillator, a beatfrequency oscillator and a variable frequency low power transmitter. Thecircuit is also adapted for use as a Q meter; in the measurement ofinductance, capacity and resistance at radio frequencies with anaccuracy, for instance, of..01% at 4.5 megacycles to 9.0 megacycles witha bandspread of kilocycles.

Fig. 1 of the drawings shows the simplest of all bandspread circuits inwhich tuning condenser I has bandspread condenser 2 connected inparalleltherewith and connected to opposite terminals of inductance 3.

In Fig. 2 I have shown the bandspread condenser 2 connected to a tap 8on inductance .3 at one side and to the terminal of the inductance atthe other side rather than directly in parallel with the tuningcondenser l as in Fig. 1. The circuits of both Figs. 1 and 2 are of theparallel tuned type. The prime disadvantage in using either circuitshown in Fig. 1 or Fig. 2 lies in the fact that the amount of bandspreador range covered by bandspread condenser 2 varies in proportion to,although not a linear proportion, and in the same direction as thefrequency, that is, it increases with an increase in resonant frequencyof the whole circuit.

In my investigations of the circuits of Figs. 1 and 2 I discovered thatwhen the bandspread condenser 2 is arranged in series with main tuningcondenser I, the action of the bandspread condenser 2 in the circuit ofFig. 3 is just the opposite of the action of bandspread condenser 2 inthe arrangement shown in Fig. 1, that is, with an increase of resonantfrequency of the whole circuit the range covered by bandspread condenser2 in the circuit of Fig. 3 is inversely proportional to the frequency,and similarly to the action of bandspread condenser 2 in the circuits ofFigs, 1 and 2, the proportion is not a linear one. The action ofbandspread condenser 2 in the circuits of Figs. 1 and 2 is directlyopposite to the action of bandspread condenser 2 in the circuits ofFigs. 3 and 4. Insofar as the bandspread condenser 2 is concerned itsaction in either of the circuits of Figs. 3 and 4 is the mirror image ofits action in the circuits of Figs. 1 and 2. The circuit of Fig. 3illustrates the main tuning condenser I arranged in series withbandspread condenser 2. In Fig. 4 I have shown an arrangement wherein itis possible to obtain a finer control of frequency by means ofbandspread condenser 2 by arranging a vernier or padder condenser 4 inparallel therewith. The vernier or padder condenser 4 connects betweenthe point 9 common to the bandspread condenser 2 and main tuningcondenser I and in circuit with inductance 3 as shown.

The circuits of Figs. 3 and 4 have the same disadvantages as those ofFigs. 1 and 2, that is, the bandspread range varies with a variation ofresonant frequency of the whole circuit.

I have verified all of the aforegoing results experimentally and fromthese investigations I action as condenser 2 of Fig. 1. Bygangingtherotors or movable elements of condensers 2a and 2b in Fig. 5 I obtainedsimultaneous control of their respective characteristics.

It is apparent from a study of the circuit of Fig. 5 that one of theelements of the bandspread condenser 2a is 1 connected to the same pointon the inductance 3 as one of the elements of the bandspread condenser2b. This fact occasioned me to further reason that as it was necessaryto gang the rotors of condensers 2a and 2b to obtain simultaneouscontrol, it should be possible to utilize a single condenser having twostationary elements and one rotating or movable element or in otherwords a split-stator or dual condenser. This I did as shown in Fig. 1 ofmy copending application for Letters Patent Serial No. 505,048, filedOctober 5, 1943, now Patent No. 2,400,895, granted May 28, 1946. Furtherstudy and research has resulted in the development of the circuitsherein depicted in Figs. 6-17.

Referring to Fig. 6 the functions of condenser 2'of Fig. 2 and condenser2 of Fig. 3 have been combined in one condenser I 8 in Fig. 6 which hasbut one rotor and one stator. This is made "possible by the tap 8 on theinductance 3, which must be placed just right to obtain equal bandspreadat either end of the tuning range of condenser I. The condenser Iconnects across a portion of the inductance 3 between tap 8 and one endof the inductance while condenser I8 connects with condenser I as at 9and across another portion of inductance 3 between tap 8 and the otherend of the inductance 3.

Fig. 7 is the result of the combination of the circuits of Figs. 2 and4. In Fig. 7 the function of condenser 2 in Fig. 2 and the function ofcondenser 2 in Fig. 4 have been combined in a single condenser II whichhas but one rotor and one stator. As in Fig. 6 the tap 8 on theinductance 3 must be placed properly and in addition the paddercondenser 4 must have the proper capacity to enable the bandspreadcondenser II to have the same range of control at either end of thetuning range of the condenser I. Condenser I is connected in efiectacross one portion of in ductance 3 between tap 8 and one end ofinductance 3. Condensers 4 and I I are in effect connected in paralleland connected at one end with condenser I as at 9 and across anotherportion of inductance 3, that is, between the tap 8 and the other end ofinductance 3.

Fig. 8 is a variation of Fig. '7 wherein the control range of condenserII may be varied by adjusting the condenser I2. Condenser I is in effectconnected across one portion of inductance 3, that is, between tap 8 andone end of inductance 3. Condensers II and I2 are in effect connected inseries and the combination connected in parallel with condenser 4. Thecombination thus formed is connected at one end with condenser I as at 9and is connected across another portion of inductance 3, that is,between tap 8 and the other end of inductance 3.

The circuits of Figs. 5 and 6 have a serious but correctible fault whichis that as the frequency is varied from the minimum to the maximum, orvice versa, attainable with any particular set of components the rangeof control exerted by the combined and simultaneous action 1 ofcondensers 2a and 2b and/or the con-denser I0 varies slightly, being aminimum at mid frequency and a maximum at the minimum or maximumfrequency points. This defect is serious if accurate work is to be donewith the circuit and may be corrected by the inclusion of one or morecondensers which may be adjusted either separately or automatically inunison with a variation or rotation of condenser I.

A slight variation of condenser 4 in Fig. 7 or variation of either oneor both of the condensers 4 and I2 of Fig. 8 can be made to compensatefor the lack of uniformity of the control range of condenser II ineither circuit. The lack of uniformity of the control range of thebandspread condenser II is common to all of the circuits shown if nomeans Were provided to compensate for this defect or if the means wereprovided but not used.

Fig. 9 is a diagram of a circuit in which such denser I4. Condenser l isin effect connected across one portion of inductance 3 between tap 8 andone end of inductance 3. Condensers 4, II and I4 are in effect connectedin parallel and connected at one side with condenser I as at 9. Thecombination thus formed is connected across another portion ofinductance 3 between tap 8 and the other end of inductance 3.

In Fig. 10 which is an elaboration of the circuit of Fig. 9 thecondenser I5 has been inserted aeesgme.

to providea means of adjusting the amount of compensation "provided bythe condenser I4. Condenser- I isinefiect connected across one portionof inductance 3 between tap 8 and one end of the inductance 3.Condensers I4 and I5 are in "effect connected in series. The seriescombination is in effect connected in parallel with condensers 4 and II,This combination is connected at one side with one side of condenser Ias at 9. The circuit thus formed by condensers 4, "-I I; I4 and I5 isconnected in parallel with another portion ofinductance 3, that is,between tapB and the other end of inductance 3.

Fig;"11 is a combination of Figs. 8 and in which th'econdenser I2 is thebandspread range adjustment and the condenser I5 is the ccmpen" sationadjusting means. As it is necessary that the condenser 4 and the tap 8be adjusted with respect to each other in such a Way that the controlrange of condenser II is equal at both the minimum and maximumfrequencies to which the circuit is tunable, it was also necessary tofind a practicable means of doing so. Condensers I4 and I5 are in effectconnected in series. Condensers II- and I2 are also in effect connectedin series. Both of these series paths are con-- nected in parallel andare connected in parallel with condenser 4. The combination thusestablished is connected at one side with condenser I as atll.Thecombination is also connected inparallel with another portion ofinductance 3 between tap 8 and the other end of inductance 3.

The circuits of Figs. 12-14 are variations of the circuit of Fig. 10,the difference being that the condensers I6 and I7 have been inserted toallow the bandspread or frequency range of condenser II to be adjustedso that it is equal at the minimum and maximum tunable frequencies ofthe whole circuit. The circuit of Fig. 12 allows adjustment of thecontrol range of con denser II by means of condenser I6 at the minimumfrequency to which the circuit is tunable while the circuit of Fig. 13allows adjustment of the control rangeof condenser II at itsmaximum'tunable frequency by means of condenser I I. The circuit of Fig.14 is a combination of the circuits of Figs. 12 and 13embodying all oftheir characteristics plus a greater ease of adjustment.

In Fig. '14 the inductance for the system is illustrated at 3 connectedto main tuning condenser I, in serieswith the Vernier or padder orminimum frequency adjustment condenser 4. Thus a series path is providedthrough inductance 3, main condenser I and the padder condenser 4. A tap8 on inductance 3 connects through the pair of adjustable trimmercondensers I6 and H to the mid-tap 9 between main condenser I and paddercondenser 4. Two electrical paths are provided between points in thecircuit I6-II and a point between adjustable Vernier or padder condenser4 and the terminal of inductance 3. One of these paths includes thevariable condenser I I and the other path in cludes variable condensersI4I 5.

In adjusting the circuit main condenser I is set in a maximum capacityposition. Condensers I6 and I! are set at approximately half capacitypositions. Condenser II and condensers I4--Ili are set at approximatelymaximum capacity positions. The procedure then contemplates theadjustment of condenser 4 to render the circuit responsive to apredetermined minimum frequency; 1 With maincondenser I set at maximumcapacity position, condenser I6 is then adjusted: so that condenser IIhas the proper frequency coverage between its minimum and maximumcapacity. Condenser I1 is then adjustedso that condenser II has the samecoverage at the high end of the spectrum as it did at the lower end ofthe spectrum under control of theadjustable condenser I6.- Condenser I4is then adjusted to minimum capacity position and condenser I isadjusted so that the circuit is responsive toa frequency mid-way betweenits maximumand minimum frequency. Condenser II is then adjusted fromminimum to maximum capacity-t0- determine if it has the same frequencycoverage as it had at the maximum or minimum frequencies of the circuit.If condenser I4'can be set at any point between one-half maximumcapacity and minimum capacity so that condenser II has this coverage,the circuit can be considered as adjusted and the dials on the variouscondensers correspondingly calibrated.

The circuit of Fig. 15 is identical to the circuit of Fig. 14 with theexception that condenser I has been mechanically connected to condenserI4 by means of linkage I8 so that the compensation condenser I4 may besimultaneously and automatically adjusted with the -main tuningcondenser I.

Fig. 16 depicts a circuit embodying'the characteristics of Fig. 15 plusthe condenser I9. which is adjustabletoset the minimum capacity and/orthe maximum frequency of the circuit. 1 The condenser I9 may alsorepresent the minimum capacity of the circuit, i. e., the straycapacities always present in any circuit. In Fig. 16 the circuitelements described in connection with Fig. 14 are al1 arranged asheretofore explained and in addition main condenser I and variablecondenser I4 are interconnected as represented at I8 for simultaneousadjustment. Also the additional condenser I 5 in series with the pathcontaining condenser I4 more effectively adjusts the compensationcapacity path through condenser I4. Condensers I and I4 are initiallyadjusted as described in connection with Fig. 14 and thereaftersimultaneously controlled through the cascade control represented at I8.The tape on inductance 3 may be made adjustable in the several circuitshereinbefore described.

The circuit of Fig. 1'7 is a variation of the circuit of Fig. 16 whereinthe tap 8 0n the induc tance 3 has been omitted and a small inductance20 added. This inductance 2B- is coupled to the inductance 3 in such amanner that the net effect of said inductance 20 is the same as if thetap 8 were used instead, as in the other figures. The inductance 20 maybe either fixed or adjustably coupled to inductance 3, in the lattercase the efiect is the same as if tap 8 were adjustable in the otherfigures. If inductance 2!! is adjustable, it is possible to omitcondenser I1.

It is apparent that the Figs. 15, 16 and 17 are refinements of thecircuit of Fig. 14, but these same refinements may be applied to any ofthe other circuit of any of the other figures.

If compensation is used all of the circuits from Fig. 7 to and includingFig. 17 may be adjusted to obtain the same net results provided theproper components are chosen in each case.

The valuesof the components of a typical oscillation circuit such as inFigs. 14 or 16 are:

I=325 micro=micro-farad variable condenser. I I I and I 4:100micro-micro-farad variable condenser.

3=Inductance 8.7 micro-henries tapped one-third number of turns from endof coil to which Hand l4 are connected.

4:100 micro-micro-farad adjustable Vernier or padder condenser.

l5, I6, I! and |9 =3-3o micro-micro-farad trimmer condensers.

The circuit arrangements of my invention have been found very practicalin construction and production and economical in the use of equipment.Variable condensers of customary construction may be employed in thecircuits of my invention herein and it is unnecessary to utilize anyspecial form of dual condenser which inherently involves an insulationproblem requiring substantial electrical insulation between theadjustable member and one end of the tuning inductance. Approximately10% may be saved on parts costs in the circuit arrangements shown inFigs. 6-l7 over that possible in circuits which en1 ploy a dualcondenser.

The oscillation control circuits of my invention are intended to beconnected to the input and/or output systems of electron tube circuitsfor sustaining the oscillations developed in the tunable circuits atsubstantially constant frequency.

Automatic compensation may be accomplished in all of the circuits of myinvention from Fig. '7 to Fig. 1'7 inclusive by simultaneous control ofcondensers l and 6 or I and It. The minimum capacity setting condenseris may be included in any of the circuits and depending on thecriticalness of its setting may be incorporated n shunt with any portionof the whole of inductance The inductance of Fig. 17 may be utilized inany of the circuits. The circuits of Figs. '7 to 17 inclusive are eachindividually important, as each with properly proportioned componentsmay be utilized with considerable effectiveness.

While I have described my invention in certain of its preferredembodiments, I realise that mod"- fications may be made and I desirethat it be understood that I intend no limitations upon my inventionexcept as may be imposed by the following claims.

What I claim and desire to secure by Letters Patent of the United Statesis as follows:

1. An oscillation control circuit comprising an inductance, a maintuning condenser, a Vernier condenser, a series path electricallyconnected to include said main condenser and said Vernier condenseracross said inductance, a tap intermediate said main condenser and saidVernier condenser, a coupling inductance coupled to the aforesaidinductance and electrically connected to that portion of the inductancewhich connects to the ser es path that includes said main condenser andsaid Vernier condenser and a circuit connection extending from the otherend of said coupling inductance to said tap intermediate said maincondenser and Vernier condenser.

2. An oscillation control circuit comprising an inductance, a maintuning condenser, a Vernier condenser, a series path electricallyconnected to include said main condenser and said Vernier condenseracross said inductance, a tap intermediate said main condenser and saidvernier condenser, a coupling inductance coupled to the aforesaidinductance and electrically connected to that portion of the inductancewhich connects to the series path that includes said main condenser andsaid Vernier condenser, a circuit connection extending from the otherend of said coupling inductance to said tap intermediate said maincondenser and said Vernier condenser and tuning means connected betweensaid circuit connection and one side of the series path which connectsbetween said main condenser, said vernier condenser and said firstmentioned inductance.

3. An oscillation control circuit-comprising an inductance, a maintuning condenser, a Vernier condenser, a series path electricallyconnected to include said main condenser and said Vernier condenseracross said inductance, a tap intermediate said main condenser and saidVernier condenser, a coupling inductance coupled to the aforesaidinductance and electrically connected to that portion of the inductancewhich connects to the series path that includes said main condenser saidVernier condenser, a circuit connection extending from the other end ofsaid coupling inductance to said tap intermediate said main condenserand said Vernier condenser, tuning means connected between said circuitconnection and one side of the series path which connects between saidmain condenser, said Vernier condenser and said mentioned inductance,band spread tunin means connected between said circuit connection andthe last mentioned portion of said inductance in parallel with saidtuning means, and means for simu1ta necusly adjusting said tuning meansand said main tuning condenser.

4. oscillation control circuit comprising an inductance, a main tuningcondenser, a vernier c-onder a series path electrically connected toll'lCiLllle said main condenser and said Vernier .enser across saidinductance, a tap intertte said main condenser and said Verniercondenser, a coupling inductance coupled to the aio caid inductance andelectrically connected to that portion of the inductance winch connectsto the series path that includes said main condenser and said Verniercondenser, a circuit connection extending from the other end of saidcoupling inductance to said tap intermediate said main condenser andsaid Vernier condenser, tuning means connected between said circuitconection and one side of the series path which connects between saidmain condenser, said vernier condenser and said first mentionedinductance, and a condenser disposed in said circuit connection on eachside of the point of connection of said tuning means thereto, one ofsaidv last ment ned condensers being connected with said coupl 1ginductance and the other of said last mentioned condensers beingconnected to the tap intermediate said main tuning condenser and saidVernier condenser.

5. An oscillation control circuit comprising an inductance, a maintuning condenser, a Vernier condenser, a series path electricailyconnected to include said main condenser and said Vernier condenseracross said inductance, a tap inter mediate said main condenser and saidVernier condenser, a coupling inductance coupled to the aforesaidinductance and electrically connected to that portion of the inductancewhich connects to the series path that includes said main condenser andsaid Vernier condenser, a circuit connection extending from the otherend of said coupling inductance to said tap intermediate said maincondenser and said Vernier condenser, tunin means connected between saidcircuit connection and one side of the series path which connectsbetween said main condenser, said Vernier condenser and said firstmentioned inductance, a condenser disposed in said circuit connection oneach side of the point of connection of, said tuning 10 means thereto,one of said last mentioned condensers being connected with said couplingin- REFERENCES CITED ductance and the other of said last mentioned h fll win references are of record in the condensers being connected to thetap intermefile Of this p nt! diate said main tuning condenser and saidVernier 5 UNITED STATES PATENTS condenser, band spread tuning meansconnected between said circuit connection and the common Number NameDate ends of said inductances and means for simul- ,8 7 Jelen Jan. 24,1933 taneously adjusting said tuning means and said 1, 3 ,657 Hansel!Dec. 12, 1933 main tuning condenser. 10 2,062,379 Silver Dec. 1, 19362,207,254 Holst et a1 July 9, 1940 GEORGE s. WACH'I'MAN. 2,309,014 RootJan. 19, 1943

